Comparison of cadmium biosorption by Gram-positive and Gram-negative bacteria from activated sludge

Summary Gram-positive and Gram-negative bacteria were isolated from activated sludge and used to evaluate differences in cadmium biosorption. Gram-positive bacteria exhibited approximately 20% more cadmium biosorption at 30°C and pH 6.6 than Gram-negatives. Biosorption was largely passive in both cases, although metabolic uptake appeared to occur to a higher extent with Gram-positive bacteria.     

Copper biosorption by Pseudomonas cepacia and other strains

Biosorption of copper by Pseudomonas cepacia was found to be dependent on added copper concentration. Copper uptake by the cells was rapid over the range of copper concentrations tested and complete within the first 10 min of incubation time. The effect of pH on copper uptake by P. cepacia was determined using overlapping buffers over the pH range 3–8, and copper biosorption from a 10 mM copper solution was greatest at pH 7. Copper uptake (measured by analysis of cell digests) was unaffected by cyanide and azide (up to 30 mM) and by incubation of cells with a 10 mM copper solution at 4 °C. Evidence from these results suggested that copper uptake by P. cepacia cells involves surface binding and not intracellular accumulation by active transport. Biosorption of copper by various Pseudomonas isolates from metal-contaminated environments agreed well with copper biosorption by Pseudomonas strains from the National Collection of Type Cultures (NCTC).     

Comparative study of Cd(II) and Cr(VI) biosorption on Staphylococcus xylosus and Pseudomonas sp. in single and binary mixtures

Biosorption of Cd(II) and Cr(VI) ions in single solutions using Staphylococcus xylosus and Pseudomonas sp., and their selectivity in binary mixtures was investigated. Langmuir and Freundlich models were applied to describe metal biosorption and the influence of pH, biomass concentration and contact time was determined. Maximum uptake capacity of cadmium was estimated to 250 and 278 mg g(-1), whereas that of chromium to 143 and 95 mg g(-1) for S. xylosus and Pseudomonas sp., respectively. In binary mixtures with Cd(II) ions as the dominant species, there is a profound selectivity for cadmium biosorption, reaching 96% and 89% for Pseudomonas sp. and S. xylosus, respectively, at 10 mg l(-1) Cd(II) and 5 mg l(-1) Cr(VI). Interesting, when chromium (VI) ions are the dominant species, there is selectivity towards chromium around 92% with S. xylosus only.     

Cadmium biosorption by Streptomyces pimprina waste biomass

Biosorption of cadmium from solution was studied using a hamycin-producing Streptomyces pimprina waste biomass. Mycelial pretreatments with 80% ethanol increased the uptake of cadmium threefold. The rate of uptake of the metal was maximum in the first 10 min and the equilibration of the system was achieved after 60 min. At pH 2.0 there was no adsorption of cadmium; however, as the pH of the solution increased, a rise in the adsorption could be noticed, which peaked at pH 5.0. The uptake of cadmium was found to increase linearly as a function of cadmium concentration up to 500 mg/l. The data could be fitted to Freundlich and Langmuir models for absorption processes. A 0.1 M EDTA solution could desorb cadmium loaded on S. pimprina biomass with the highest efficiency.     

Cadmium removal from simulated wastewater to biomass byproduct of Lentinus edodes

A kind of agricultural waste, the byproduct of brown-rot fungus Lentinus edodes, was used as an efficient biosorbent for the removal of cadmium from water in this paper. The sorption conditions, such as pH, the dose of biomass and the initial concentration of cadmium were examined. Three kinds of adsorption models were applied to simulate the biosorption data. Uptake of cadmium was higher in weak acid condition than in strong acid condition. Nearly no sorption of cadmium occurred when the pH value was lower than 2.5. Biosorption isothermal data could be well simulated by Freundlich model, and then Langmuir and Temkin model. Langmuir simulation of the biosorption showed that the maximum uptake of cadmium was 5.58mmol/g in weak acid condition, which was much higher than many other biosorbents. The exchanged proton was highly related to the uptake of cadmium in weak acid condition. Fourier transform infrared spectrums and energy-dispersive X-ray microanalyzer were used to reveal ion-exchange mechanism between cadmium and the functional groups or participated inorganic metal ions during biosorption.     

Heavy metal removal from aqueous solution by wasted biomass from a combined AS-biofilm process

This study evaluated the capability of metal biosorption by wasted biomass from a combined anaerobic-anoxic-oxic (A2O)-biofilm process with simultaneous nitrogen and phosphorus removal. Zinc, cadmium and nickel were rapidly adsorbed in 20 min by the harvested sludge from a continuous-flow pilot-plant. Biosorption equilibrium was then reached in 6h. The biosorption isotherm showed that metal biosorption behavior had fitted well to the Freundlich isotherm, but not Langmuir isotherm. The capacity constants k of Freundlich model for nickel, zinc and cadmium were 0.471, 0.298 and 0.726, respectively; the affinity constants 1/n were 0.444, 0.722 and 0.718, respectively. The order of metal affinity for the wasted biomass was Zn > Cd > Ni, which was in conformity to the other biosorption results with different biological sludge.     

Biosorption of copper(II) ions onto powdered waste sludge in a completely mixed fed-batch reactor: estimation of design parameters

Biosorption of Cu(II) ions onto pre-treated powdered waste sludge (PWS) was investigated using a fed-batch operated completely mixed reactor. Fed-batch adsorption experiments were performed by varying the feed flow rate ( 0.075-0.325 l h(-1)), feed copper (II) ion concentrations (50-300 mg l(-1)) and the amount of adsorbent (1-6 g PWS) using fed-batch operation. Breakthrough curves describing the variations of effluent copper ion concentrations with time were determined for different operating conditions. Percent copper ion removals from the aqueous phase decreased, but the biosorbed (solid phase) copper ion concentrations increased with increasing the feed flow rate and Cu(II) concentration. A modified Bohart-Adams equation was used to determine the biosorption capacity of PWS and the rate constant for Cu(II) ion biosorption. Adsorption rate constant in fed-batch operation was an order of magnitude larger than those obtained in adsorption columns because of elimination of mass transfer limitations encountered in the column operations while the biosorption capacity of PWS was comparable with powdered activated (PAC) in column operations. Therefore, a completely mixed reactor operated in fed-batch mode was proven to be more advantageous as compared to adsorption columns due to better contact between the phases yielding faster adsorption rates.     

Removal of cadmium(II) ion from aqueous system by dry biomass, immobilized live and heat-inactivated Oscillatoria sp. H1 isolated from freshwater (Mogan Lake)

Oscillatoria sp. H1 (Cyanobacteria, microalgae) isolated from Mogan Lake was used for the removal of cadmium ions from aqueous solutions as its dry biomass, alive and heat-inactivated immobilized form on Ca-alginate. Particularly, the effect of physicochemical parameters like pH, initial concentration and contact time were investigated. The sorption of Cd(II) ions on the sorbent used was examined for the cadmium concentrations within the range of 25-250 mg/L. The biosorption of Cd(II) increased as the initial concentration of Cd(II) ions increased in the medium up to 100 mg/L. Maximum biosorption capacities for plain alginate beads, dry biomass, immobilized live Oscillatoria sp. H1 and immobilized heat-inactivated Oscillatoria sp. H1 were 21.2, 30.1, 32.2 and 27.5 mg/g, respectively. Biosorption equilibrium was established in about 1 h for the biosorption processes. The biosorption was well described by Langmuir and Freundlich adsorption isotherms. Maximum adsorption was observed at pH 6.0. The alginate-algae beads could be regenerated using 50 mL of 0.1 mol/L HCl solution with about 85% recovery.     

Biosorption of Copper(II) by Live and Dried Biomass of the White Rot Fungi Phanerochaete chrysosporium and Funalia trogii

Biosorption is an innovative and alternative technology to remove heavy metal pollutants from aqueous solution using live, inactive and dead biomasses such as algae, bacteria and fungi. In this study, live and dried biomass of Phanerochaete chrysosporium and Funalia trogii was applied as heavy metal adsorbent material. Biosorption of copper(II) cations in aqueous solution by live and dried biomass of Phanerochaete chrysosporium and Funalia trogii was investigated to study the effects of initial heavy metal concentration, pH, temperature, contact time, agitation rate and amount of fungus. Copper(II) was taken up quickly by fungal biomass (live or dried) during the first 15 min and the most important factor which affected the copper adsorption by live and dried biomass was the pH value. An initial pH of around 5.0 allowed for an optimum adsorption performance. Live biomass of two white rot fungi showed a high copper adsorption capacity compared with dried biomass. Copper(II) uptake was found to be independent of temperature in the range of 20–45 °C. The initial metal ion concentration (10–300 mg/L) significantly influenced the biosorption capacity of these fungi. The results indicate that a biosorption as high as 40–60 % by live and dried biomass can be obtained under optimum conditions.     

Immobilization of blue green microalgae on loofa sponge to biosorb cadmium in repeated shake flask batch and continuous flow fixed bed column reactor system

Summary An indigenous strain of blue green microalga, Synechococcus sp., isolated from wastewater, was immobilized onto loofa sponge discs and investigated as a potential biosorbent for the removal of cadmium from aqueous solutions. Immobilization has enhanced the sorption of cadmium and an increase of biosorption (21%) at equilibrium was noted as compared to free biomass. The kinetics of cadmium biosorption was extremely rapid, with (96%) of adsorption within the first 5 min and equilibrium reached at 15 min. Increasing initial pH or initial cadmium concentration resulted in an increase in cadmium uptake. The maximum biosorption capacity of free and loofa immobilized biomass of Synechococcus sp. was found to be 47.73 and 57.76 mg g⁻¹ biomass respectively. The biosorption equilibrium was well described by Langmuir adsorption isotherm model. The biosorbed cadmium was desorbed by washing the immobilized biomass with dilute HCl (0.1 M) and desorbed biomass was reused in five biosorption–desorption cycles without an apparent decrease in its metal biosorption capacity. The metal removing capacity of loofa immobilized biomass was also tested in a continuous flow fixed-bed column bioreactor and was found to be highly effective in removing cadmium from aqueous solution. The results suggested that the loofa sponge-immobilized biomass of Synechococcus sp. could be used as a biosorbent for an efficient removal of heavy metal ions from aqueous solution.     

Lead biosorption by different morphologies of fungus Mucor indicus

Biosorption characteristics of Pb⁺² ions from aqueous solution were investigated using fungus Mucor indicus biomass treated with NaOH. Biosorption was measured as a function of biomass morphology, pH, biomass concentration, contact time, and metal concentration. The morphology of M. indicus biomass was manipulated towards filamentous or yeast-like forms. The highest and lowest biosorption capacities were observed for purely filamentous and yeast-like forms, respectively. Models of Langmuir, Freundlich, Temkin, and Scachard were applied to describe adsorption isotherm and fitted appropriately. Biosorption kinetics was successfully described using Ho’s pseudo-second-order model. Maximum and minimum values of biosorption capacity of Pb²⁺ were 22.1 and 12.1 mg g⁻¹ for purely filamentous and yeast-like morphologies, respectively. Increasing pH resulted in higher biosorption of Pb⁺² ions up to pH 5.5. Biosorption capacity of individual Pb⁺² ions was reduced in the presence of other metal ions in bi- or multi-metal ion experiments. Metal ions adsorption by the biomass could be eluted effectively with HNO₃.     

Biosorption of Pb(II) and Cu(II) by activated sludge in batch and continuous-flow stirred reactors

Biosorption of Pb(II) and Cu(II) ions in single component and binary systems was studied using activated sludge in batch and continuous-flow stirred reactors. In biosorption experiments, the activated sludge in three different phases of the growth period was used: growing cells; resting cells; dead or dried cells. Because of the low adsorption capacity of the non-viable activated sludge especially in the case of Pb(II) ions, biosorption of the Cu(II) and Pb(II) ions from the binary mixtures was carried out by using the resting cells. The biosorption data fitted better with the Freundlich adsorption isotherm model. Using a mathematical model based on continuous system mass balance for the liquid phase and batch system mass balance for the solid phase, the forward rate constants for biosorption of Pb(II) and Cu(II) ions were 0.793 and 0.242 1 (mmolmin)(-1), respectively.     

土生鳞伞对Cd2+的吸附特性

以土生鳞伞（Pholiota terrestris Overh.）子实体为生物吸附剂吸附水溶液中的Cd2+,分析吸附剂用量、初始pH值、初始重金属浓度、反应时间这4个因素对吸附的影响,并采用Langmuir和Freundlich等温吸附模型及准一级、准二级动力学模型拟合土生鳞伞的生物吸附特性.结果表明:水溶液中Cd2+...     

Biosorption of uranium(VI) by Aspergillus fumigatus

Aspergillus fumigatus removed uranium(VI) very rapidly and reached equilibrium within 1 h of contact of biomass with the aqueous metal solution. Biosorption data fitted to Langmuir model of isotherm and a maximum loading capacity of 423 mg U g^–1 dry wt was obtained. Distribution coefficient as high as 10,000 (mg U g^–1)/(mg U ml^–1) at a residual metal ion concentration of 19 mg l^–1 indicates its usefulness in removal of uranium(VI) from dilute waste streams. Optimum biosorption was seen at pH 5.0 and was independent of temperature (5–50°C ). Initial metal ion concentration significantly influenced uptake capacity which brought down % (w/w) uranium(VI) removal from 90 at 200 mg U l^–1 to 35 at 1000 mg U l^–1. Presence of 0.84 mmol Fe²⁺, Fe³⁺, Ca²⁺ and Zn²⁺ had no effect on uranium(VI) biosorption unlike Al³⁺ (0.84 mM) which was inhibitory.     

Application of dried sewage sludge as phenol biosorbent

The aim of this work was to determine the potential application of dried sewage sludge as a biosorbent for removing phenol from aqueous solution. Results showed that biosorption capacity was strongly influenced by the pH of the aqueous solution with an observed maximum phenol removal at pH around 6-8. Biosorption capacity increased when initial phenol concentration was increased to 110 mg/L but beyond this concentration, biosorption capacity decreased suggesting an inhibitory effect of phenol on biomass activity. Biosorption capacity decreased from 94 to 5 mg/g when biosorbent concentration was increased from 0.5 to 10 g/L suggesting a possible competitive effect of leachable heavy metals from the sludge. The effect of Cu2+ on biosorption capacity was also observed and the results confirmed that the phenol biosorption capacity decreased when concentration of Cu2+ in the sorption medium was increased up to 15 mg/L. Desorption of phenol using distilled deionized water was less than 2% suggesting a strong biosorption by the biomass.     

Heavy metal biosorption by biomass of Ochrobactrum anthropi producing exopolysaccharide in activated sludge

The removal of chromium, cadmium and copper, toxic metals of high environmental priority due to their toxicity, from dilute aqueous solutions has been studied in the present work, applying a dead exopolysaccharide producing bacterium, Ochrobactrum anthropi, isolated from activated sludge. Particularly, the effect of pH, metal concentration and the effects of contact time were considered. Optimum adsorption pH values of chromium(VI), cadmium(II) and copper(II) were 2.0, 8.0 and 3.0 respectively. Experimental results also showed the influence of initial metal concentration on the metal uptake for dried biomass. Both the Freundlich and Langmuir adsorption models were suitable for describing the short-term biosorption of chromium(VI), cadmium(II) and copper(II) by O. anthropi.     

Kinetic and equilibrium modeling of chromium (VI) biosorption on fresh and spent Spirulina platensis/Chlorella vulgaris biomass

Biosorption of chromium (VI) was studied using both fresh and spent algal biomass of Spirulina platensis and Chlorella vulgaris. Both showed comparable behavior suggesting that biosorption is primarily a surface phenomenon. Biosorption rate was very fast during the first five minutes, in which almost 50% of the chromium (VI) was adsorbed. Two step kinetic model was proposed for biosorption. Equilibrium data obeyed Freundlich and Langmuir adsorption isotherms. Fresh algal biomass of S. platensis gave maximum of 73.6% biosorption of chromium (VI) in 100 ppm solution at 1 g l(-1) cell loading. For improved economics, beta-carotene was extracted from S. platensis and the spent biomass was used for chromium (VI) biosorption. The maximum biosorption by spent biomass was increased to 86.2%. Thus, this two step process not only showed improved efficiency in biosorption ( approximately 17% increase) but also gave valuable byproduct, namely beta-carotene.     

Entrapment of white-rot fungus Trametes versicolor in Ca-alginate beads: preparation and biosorption kinetic analysis for cadmium removal from an aqueous solution

The biosorption of cadmium ions onto entrapped Trametes versicolor mycelia has been studied in a batch system. The maximum experimental biosorption capacities for entrapped live and dead fungal mycelia of T. versicolor were found as 102.3 +/- 3.2 mg Cd(II) g(-1) and 120.6 +/- 3.8 mg Cd(II) g(-1), respectively. Biosorption equilibrium was established in about 1 h and biosorption was well described by the Langmuir and Freundlich biosorption isotherms. The change in the biosorption capacity with time was found to fit the pseudo-second-order equation. Since the biosorption capacities were relatively high for both entrapped live and dead forms, those fungal forms could be considered as suitable biosorbents for the removal of cadmium in wastewater-treatment systems. The biosorbents were reused in three consecutive adsorption/desorption cycles without a significant loss in the biosorption capacity.     

Equilibrium and kinetic studies on biosorption potential of charophyte biomass to remove heavy metals from synthetic metal solution and municipal wastewater

The risk of heavy metal contamination in domestic water causes serious health and environmental problems. Biosorption has been considered as an efficient and alternative way for treatment of heavy metal–contaminated wastewater. The potentials of dried charophytes, Chara aculeolata and Nitella opaca, to biosorb lead (Pb), cadmium (Cd), and zinc (Zn) from synthetic solutions and municipal wastewater were investigated. The efficiency of metal removal was studied under varied conditions in different sorbent dosages, pH, and contact times. Biosorption isotherm and kinetics were used to clarify heavy metal preference and biosorption mechanism. C. aculeolata and N. opaca performed well in the biosorption of all three metal ions, with preference towards Pb, followed by Cd and Zn, in the single-metal solutions. Pb adsorption onto algal biomass followed first-order rate kinetics (N. opaca) and intraparticle diffusion (C. aculeolata and N. opaca). These results indicated physical adsorption process between Pb ions and both algal biomasses. Cd and Zn biosorption kinetics fitted the second-order rate model, indicating chemical adsorption between metal ions and both algae. The experimental data of three-metal biosorption fitted well to Langmuir isotherm model, suggesting that the metal ion adsorption occurred in a monolayer pattern on a homogeneous surface. C. aculeolata exhibited slightly higher maximum uptake of Pb, Cd, and Zn (105.3 mgPb/g, 23.0 mgCd/g, 15.2 mgZn/g) than did N. opaca (104.2 mgPb/g, 20.5 mgCd/g, 13.4 mgZn/g). In multi-metal solutions, antagonistic effect by metal competition was observed. The ability of charophytes to remove Pb and Zn was high in real municipal water (81–100%). Thus, the charophytic biomass may be considered for the treatment of metal contamination in municipal wastewater.     

Sites of cadmiun uptake in bacteria used for biosorption

Summary Electron microscopy and x-ray spectroscopy were used to determine location and type of cadmium biosorption on and in bacteria, some of which produced extracellular polymers. Examined Arthrobacter and Pseudomonas species appear to have detoxification systems that precipitate cadmium internally irrespective of whether of not they excrete polymers. Capsular Klebsiella aerogenes strains showed minimal intracellular uptake but over a 5–100 mg dm^–3 Cd range produced the highest net metal removal levels due to significant extracellular adsorption. Offprint requests to: J. A. Scott